FR2996782A1 - CATALYST DENSE LOADING SYSTEM IN BAIONNETTE TUBES FOR VAPOREFORMING EXCHANGER REACTOR USING REMOVABLE DEFLECTORS - Google Patents

Abstract

The present invention describes a device and a method for dense and homogeneous catalyst loading in the annular space (4) of bayonet tubes defined by an outer tube (6) and an inner tube (5), said device consisting of a set of removable deflectors (7) and implemented in a steam reforming reactor.

Description

FIELD OF THE INVENTION The present invention is in the field of the loading of catalytic tubes used in tubular reactors employing highly endothermic or strongly exothermic reactions. The present invention is therefore particularly suitable for the steam reforming reactor of natural gas or various hydrocarbon cuts for the production of the CO + H2 mixture called synthesis gas. There are two main families of steam reforming reactors. Reactors in which the heat is supplied by a set of burners located inside the reactor, and those in which the heat is supplied by a coolant generally combustion fumes, said combustion taking place outside the reactor of steaming itself. Some reactors of the latter type which is called in the following reactor exchanger, use simple tubes. Others use double tubes also called bayonet tubes. A bayonet tube can be defined as an inner tube surrounded by an outer tube coaxial with the inner tube, the annular space between the inner tube and the outer tube being generally filled with catalyst. In the rest of the text we will speak of annular space or catalytic zone to designate said annular space defined by the bayonet tubes. In the context of the present invention, the natural gas or more generally the hydrocarbon feedstock is introduced through the annular zone in a flow from top to bottom, and the reaction effluents are collected in the central part of the inner tube in a bottom flow. high. A reverse flow direction of the feedstock and reaction effluents is also possible. The reaction of steam reforming of natural gas for the production of hydrogen is very endothermic and therefore generally takes place in furnaces or reactors-exchangers in the previously defined sense. The reaction takes place at very high temperatures, typically 900 ° C and under pressure, typically 20 to 30 bar. Under these conditions, only an implementation of the reaction inside tubes can be considered under economically viable conditions because of the mechanical strength of the materials.

The catalytic exchanger reactors thus consist of a multitude of tubes, typically of the order of 200 to 350 tubes for units producing 100,000 Nm 3 / h of hydrogen, this set of tubes being enclosed in a shell which receives the fluid. hot enough to provide the necessary calories for the steam reforming reaction.

This hot fluid or heat transfer fluid is generally constituted by the fumes of a combustion occurring outside the exchanger reactor. The catalyst must therefore be installed in all steam reforming tubes regularly from one tube to another, in order to have the same pressure drop from one tube to the other. This condition is very important in order to ensure a good distribution of the reagents on all the catalytic tubes and to prevent a tube being, for example, less fed, which could lead to significant overheating of the material constituting the tube, this overheating reducing 'as long as the life of the tube. Similarly, it is important that no empty space, that is to say without catalyst or depleted in catalyst, remains in a tube, because again the tube could overheat locally, for lack of catalytic reaction inside. In addition, any heterogeneity in the distribution of the catalyst in the reaction zone may result in an unbalanced flow of the reaction fluid or fluids. The device according to the present invention therefore aims at a loading both dense and homogeneous between each of the bayonet tubes forming part of the exchanger reactor. EXAMINATION OF THE PRIOR ART In a conventional reforming furnace, the traditional loading of the tubes, which have a typical inside diameter of 10 cm, is done by means of the catalyst filled bags which are open on the surface of the bed. . This method of loading is known to those skilled in the art under the name of loading "sock" and is known not to generate a high density of loading. The tubes are then manually vibrated by hammers or by a mechanical vibration system, to promote the introduction of the catalyst particles, minimize voids and thus increase the loading density. However, excessive vibration can lead to breakage of the catalyst grains, and to a significant increase in the pressure drop.

However, it is difficult with this method to make a good quality loading, and it is generally necessary to reproduce several times the vibration operation to achieve pressure losses adjacent to a tube to another. Other improved procedures and equipment have been proposed under the term UnidenseTM technology originally developed by Norsk Hydro or under the term SpiraloadTM technology developed by Haldor Topsoe. These technologies apply to single tubes and not bayonet tubes. Patent FR 2950822 of the Applicant describes a solution for loading bayonet tubes with 3 charging tubes, with mechanical brakes or pneumatic braking. This loading method allows dense and uniform loading of the bayonet tubes. As it is a "grain-by-grain" method, it proves to be too slow and unsuitable for implementation at the scale of an industrial reactor comprising several hundred tubes. In general, it can be said that many documents exist in the field of catalyst loading in steam reforming tubes. Most of them use soft slowing means or rigid obstacles in the form of inclined planes. But none of the documents found relates to an application to bayonet tubes with loading of an annular zone and avoidance of the central tube. The device which is the subject of the present invention can therefore be defined as a dense catalyst loading device in the annular zone of a bayonet tube fitted to a steam reforming exchanger reactor, the device enabling homogeneous density loading in each of the tubes of the exchanger reactor. respecting a time constraint compatible with the requirements of an industrial start. Moreover, in a certain number of cases, the device according to the invention must be able to adapt to a variation in the diameter of the outer tube, imposed by the mechanical and thermal stresses that evolve along the tube, and therefore to a change in dimensions. of the annular zone. SUMMARY DESCRIPTION OF THE FIGURES FIG. 1 represents a device according to the invention in the case where the annular zone of each bayonet tube is divided into 3 loading sectors of identical surfaces formed by the system for holding the central tube from the top of the tube. catalytic. The device comprises a common hopper (1) for the three sectors, a common conveyor belt (2) for the three sectors, a funnel (3) specific to each sector or common to the three sectors, deflectors (7) connected by chains. (8) to a winder (10), this for each of the sectors. A top view of the device allows to assess the occupancy rate of the horizontal section of a sector by the deflector. Figure 1 (A) is a side view, Figure 1 (B) is a top view, and Figure 1 (C) shows the meaning of the angles a and p. Figure 2 shows a device according to the present invention in the case where the inner tube (5) passes laterally through the outer tube (6) creating an elbow at the top which reduces the passage section to introduce the loading system. Crossing the outer tube (6) by the inner tube (5) requires to place a device that is identical to that which would be used in the case of an annular zone divided into two sectors of identical section. Figure 2 (A) is a side view, Figure 2 (B) is a top view and Figure 2 (C) shows the angle a. SUMMARY DESCRIPTION OF THE INVENTION The present invention can be defined as a dense catalyst filling device 20 in a steam reforming reactor consisting of a plurality of bayonet tubes enclosed in a shell, each bayonet tube having an annular zone at least partially filled of catalyst. Said catalyst consists of particles occupying at least part of the annular space (4) between an inner tube (5) and an outer tube (6), all of these two tubes constituting the bayonet tube, the width of said space annular 25 being between 30 mm and 80 mm, and its height being between 10 and 20 meters. The catalyst particles generally have the shape of cylinders of height approximately 10 mm to 20 mm, and diameter approximately 5 mm to 20 mm. The device according to the present invention consists in its basic version in: - a set of baffles (7) uniformly distributed vertically along the annular space (4) and separated by a vertical distance of between 50 cm and 150 cm - said baffles (7) being interconnected by a chain (8) which wraps around a reel (10) located outside the tube to be filled, and the catalyst particles being contained in - a hopper central unit (1) for delivering the particles on a treadmill or a vibrating corridor (2) feeding each sector, via a funnel (3), through which the particles flow inside the the annular space (4). In the basic version, the annular space (4) of each bayonet is not divided and the filling device according to the present invention occupies a portion of this annular space between 50% and 90%. In other variants related to the existence of a centering element of the inner tube relative to the outer tube, or linked to the passage of the outer tube (6) by the inner tube (5), the annular zone (4) of each bayonet tube is divided into a number of substantially identical areas of area extending over the entire length of the tube. Generally the number of sectors 15 will be two or three, and each sector is then equipped with a system of deflectors as described in the basic version. These deflector systems, one per sector, then form the device according to the invention. A particular case particularly frequent in the field of application of the present device is that in which the annular space (4) is traversed in its upper part by the inner tube (5) whose exit end is located at outside the outer tube (6). This crossing of the inner tube (5) is an obstacle and leads to use two baffle systems in parallel as if the annular space was divided into two sectors. Generally, each deflector is substantially in the form of a wing inclined downwards by an angle alpha (a) to the vertical of between 30 ° and 50 °, each deflector occupying a portion of the horizontal surface of the sector between 50% and 90% of the said area of the sector. In some cases, it further introduces a bend of the wing in a radial stop in the sense that this stop is in the axis of a radius. The fold is characterized by the angle beta (f3) that forms each half wing thus formed with the vertical. The angle 13 can take values of between 20 ° and 75 °, and preferably between 30 ° and 60 °. In the case where the diameter of the wall of the annular space (4) varies, due to outer tube portions (6) of decreasing diameter from top to bottom, the deflector system (7) adapts to this variation of section always respecting the condition of occupation of the said horizontal section in the range of 50% to 90% by an adjustment of the angle alpha, the smallest value being adapted to the portion of smaller diameter, and the most large value at the portion of larger diameter, the articulation of the blade of the deflector on its axis being free, and a second set of chain to raise more or less the end of the blade of the deflector so as to vary the alpha angle. Still in the case where the diameter of the wall of the annular space (4) varies, due to external tube portions (6) of decreasing diameter from top to bottom, the deflector system (7) can be provided with its ends closest to the wall of the annular space (4) of flexible rubber lips that allow to adjust the length of the blades being more or less folded, so as to maintain the load factor of the section of the annular space. A mass is then added down the chain to force the system down into the smaller diameter portion of the annular zone (4). The present invention also relates to a catalyst loading method using the previously described device, which method can be broken down into the following series of steps: the loading system is initially wound in the outer reel (10), the hopper (1) being filled with solid, the loading system is then gradually introduced into the annular zone 20 (4) by its upper part until the first deflector (7) reaches a distance from the bottom of the tube between 50 cm and 100 cm, the treadmill (2) is started to provide a solid flow rate of between 250 and 500 kg / h, which solid is introduced into the annular zone (4) or a sector of the said annular zone (4) via the funnel (3), 25 as the tube fills, the loading system is raised from the annular zone (4) using the winder external (10), so as to respect a constant distance between the first deflector (7) and the surface of the bed which is gradually constituted, said distance being between 50 cm and 100 cm, the system is wound with a speed equivalent to the loading speed of the tube 30 between 0 , 2 m / min and 0.4 m / min, once the tube loaded and the loading system wound up, the system is moved for loading the next tube.

DETAILED DESCRIPTION OF THE INVENTION The present invention can be defined as a device for the dense loading of catalyst into the annular space of bayonet tubes, each tube having a height of between 10 and 20 m, a diameter of the outer tube (6 ) between 250 mm and 150 mm, and a diameter of the inner tube (5) between 10 mm and 40 mm. The annular space containing the catalyst therefore has a characteristic width of about 50 mm. In practice, depending on the case, the characteristic width of the annular space may vary between 30 and 80 mm. In addition, in some cases the outer tube (6) has a variable diameter in sections which decreases from top to bottom, which means that the characteristic width of the annular space also decreases from top to bottom. The device according to the invention must therefore adapt to these characteristic width variations and maintain its performance on all the sections. The catalyst grains have the shape of cylinders of about 1 cm to 2 cm in height and 0.5 cm to 2 cm in diameter. One of the problems with loading them into tubes over 15 meters in length is the risk of breakage of these cylinders if they were simply dropped without any precautions, which is one of the solutions for carrying out a dense loading. . Other problems are related to the geometry of the catalytic space itself which is therefore annular, which does not allow the passage of conventional loading systems. In addition, the inner tube (5) of the bayonet is generally kept coaxial with the outer tube (6) by at least one centering piece which divides the annular space into several sectors, which prohibits the use of any device. which would surround the central tube. In some cases it is also necessary to take into account the inner tube (5) which passes through the outer tube (6) to allow a completely unobstructed exit of the reaction effluents. As previously indicated, the risk of veiling is increased when the ratio of the tube diameter to the main particle size is less than 8, which is often the case in the context of the present invention, since the typical width is the annular space (50 mm) equals about 4 times the characteristic diameter of the catalyst particles.

Finally, the loading being tube by tube (or by two to three parallel-fed tubes), it must be fast enough for industrial use, because a steam reforming reactor aiming at a production of about 100,000 Nm3 / hr. H2 has about 200 to 350 tubes.

All of these constraints are satisfied by the dense filling device according to the present invention which can be defined as follows: The present invention describes a device for dense filling of the catalyst in a steam reforming reactor consisting of a plurality of tubes bayonets enclosed in a calender, the catalyst consisting of solid grains occupying at least part of the annular space between an inner tube and an outer tube, all of these two tubes constituting a bayonet tube. The steam reforming exchanger reactor to which the present invention is directed consists of approximately 300 identical bayonet tubes with a height of between 12 and 20 meters, all of these bayonet tubes being enclosed in a shell which can reach 10 meters in length. diameter.

The width of the annular space between the inner tube and the outer tube of a bayonet tube is between 30 mm and 80 mm, and its height is between 12 and 20 meters. The catalyst particles generally have the shape of cylinders of height approximately 5 to 20 mm and diameter approximately 10 to 20 mm. The annular space thus defined may be single or divided into several substantially identical sectors by a so-called "centraliser" system. A sector is therefore defined as a portion of annular space that corresponds to a well-defined fraction of the annular section and extends over the entire height of said annular space. The filling device according to the invention consists of: - a set of baffles (7) regularly distributed vertically and separated by a vertical distance of between 50 cm and 150 cm, each baffle (7) occupying a portion of the annular section between 50% and 90%, - said baffles (7) being interconnected by a chain (8) which wraps around a reel (10) located outside the tube to be filled, and the particles of catalyst being contained in 30 - a central hopper (1) for delivering the particles on a treadmill or a vibrating corridor (2) feeding the annular space (4) (or each sector of said annular space when it is divided into sectors ), via a funnel (3), through which the particles flow inside the annular space (4). The means of transport (2) particles from the central hopper (1) to the funnel (3) can be any solid particle transport means known to those skilled in the art.

According to a first variant of the filling device according to the present invention, the annular space is divided into two or three substantially identical sectors, sectors which extend over the entire length of the bayonet tube by means of a so-called "centraliser" system arranged at the head of the annular space, each sector being equipped with an independent deflector system as described above. This amounts to saying that the device then consists of two or three identical systems acting in parallel, each deflector system occupying a sector of the annular space. In this case and preferably, the funnel (3) is specific to each sector while the treadmill (2) and the hopper (1) are common to all three sectors. According to a second variant of the filling device according to the present invention, the annular space (4) is traversed in its upper part by the inner tube (5) which constitutes an obstacle and leads to use two independent deflector systems as if The annular space was divided into two sectors. Each deflector (7) has the typical shape of a wing inclined downward from an angle alpha with respect to the vertical of between 30 ° and 50 °, each deflector occupying a portion of the horizontal surface of the sector between 50 % and 90% of the said area of the sector. In some cases, a fold of the wing is also introduced along a radial edge in the sense that this stop is located in the axis of a radius. The fold is characterized by the angle beta (13) that forms each half wing thus formed with the vertical. The angle p can take values of between 20 ° and 75 °, and preferably between 30 ° and 60 °. According to another variant of the filling device according to the present invention, the diameter of the wall of the annular space varies, defining tube portions of diameter decreasing from top to bottom. In this case, the deflector adapts to this section variation while still respecting the occupation condition of said horizontal section in the range of 50% to 90% by an adjustment of the angle alpha, the smallest value the alpha angle being adapted to the smaller diameter portion, and the larger alpha angle to the larger diameter portion. The articulation of the blade of the deflector on its vertical axis to be free, a second set of chain to raise more or less the end of the blade of the deflector so as to vary the angle alpha. Another solution to accommodate a variable annulus diameter is to use baffles provided at their ends closest to the wall of the annular space of rubber lips which adjust the length of the blades. in order to maintain the occupancy factor of the section of the annular space (4). To assist the set of deflectors in their descent, the friction of the rubber extensions to the wall of the annular space (4) can make this descent quite difficult, it is possible to provide the deflectors (7) suspended weight audit deflector. The shape of the deflectors may be arbitrary provided that the projected area of this shape in a horizontal plane respects the percentage occupancy of the horizontal section of the annular zone or sector, when the said annular zone is divided into several sectors. Generally, a deflector is in the form of a blade inclined downwards by an angle alpha of between 30 ° and 50 ° to the vertical. Another example is a flexible rubber extension of the edge of the deflector located closest to the inner wall of the annular space (4) which would keep in contact with said wall despite its diameter variation. In the case of a division of the annular space into 3 identical vertical sectors, the preferred form of the deflector is that of a wing substantially parallel to the annular sector while respecting the condition of occupation of the surface of the horizontal section within the limits of 50% to 90%. In the case of an annular space (4) not divided, but occupied at its upper end by the inner tube (5) passing through the outer tube (6), the device according to the present invention consists of two parallel deflector systems and operating independently. This system is exactly equivalent to the case of an annular space divided into two sectors. As shown in FIG. 2, it is preferable to alternate the two deflector systems so that the distance separating two consecutive deflectors (but not belonging to the same line due to this alternation) is between 25.degree. cm and 75 cm.

Regarding the method of loading using the device as described above, it can be described by the following steps: the loading system is initially wound in the outer reel (10), the hopper (1) being filled with solid, the loading system is then gradually introduced into the annular zone (4) by its upper part until the first deflector (7) reaches a distance from the bottom of the tube between 50 cm and 100 cm. the conveyor belt (2) is started so as to provide a solid flow rate of between 250 and 500 kg / h. as the tube is filled, the loading system is raised from the annular zone (4) using the external winder (10), so as to maintain a constant distance between the first deflector and the surface of the bed which is gradually constituted (we note first deflector that which is at the lowest point when the device is deployed vertically). This distance is between 50 cm and 100 cm. The system is therefore wound with a speed equivalent to the tube loading speed of between 0.2 m / min and 0.4 m / min. during loading, the hopper (1) can be refilled if its volume is smaller than that of the tube. This operation can be done with or without stopping the load. once the tube is loaded and the loading system coiled, the assembly is moved for loading the next tube. Loading verification operations, using pressure drop measurements between two points of the bayonet tube, accompany the loading operation but are not described in this text, being considered as well known in the art. skilled person.

EXAMPLE ACCORDING TO THE INVENTION The example provided corresponds to a steam reforming exchanger reactor making it possible to produce 100,000 Nm 3 / h of hydrogen.

This exchanger reactor is equipped with 300 bayonet tubes, enclosed in a calender 10 m in diameter.

Each bayonet tube consists of an outer tube (6) of diameter 128.1 mm and an inner tube (5) of diameter 42 mm. The annular space (4) therefore has a characteristic dimension of 43.05 mm. This annular space is divided into two identical radial sectors extending over the entire length of the tube, ie 14.5 m.

Each device comprises for each of the two sectors 10 deflectors separated by a vertical distance of 1 m. A deflector consists of a wing having substantially the shape of a semicircle with an outer edge of diameter 140 mm and an inner edge of diameter 35 mm. The occupancy rate for the sector section is 85%.

The angle of inclination alpha of each deflector relative to the vertical is 45 °. The loading obtained with such a system on a tube of 12 m height is characterized by the following parameters: Density of the bed: 960 kg / m3 Total loading time: 40 minutes (the two systems of deflectors for each sector operating in parallel) Variation of the pressure loss between tubes compared to the average over 5 successive loads: ± 3%.

Claims (7)

CLAIMS1) Device for dense filling of the catalyst in a steam reforming exchanger reactor consisting of a plurality of bayonet tubes enclosed in a shell, the catalyst consisting of particles occupying at least part of the annular space (4) between an inner tube ( 5) and an outer tube (6), all of these two tubes constituting a bayonet tube, the width of said annular space being between 30 mm and 80 mm, and its height of between 10 and 20 meters, the catalyst particles having the form of cylinders of height approximately 10 mm to 20 mm and diameter approximately 10 mm to 20 mm, the device consisting of: - a set of baffles (7) evenly distributed vertically along the annular space (4) and separated by a vertical distance of between 50 cm and 150 cm, - said baffles (7) being interconnected by a chain (8) which wraps around a reel (10) located outside the tube to be filled, and the catalyst particles being contained in - a central hopper (1) for delivering the particles on a treadmill or a vibrating passage (2) feeding the annular space (4), via a funnel (3) through which the particles flow within the annular space (4). 20 2) filling device according to claim 1, wherein the annular space (4) is divided into two or three substantially identical horizontal sectors, each sector extending over the entire length of the bayonet tube, by means of a so-called system. "centraliser" disposed at the head of the annular space, each sector being equipped with a system of baffles, the baffle systems being identical to each other. 25 3) filling device according to claim 1, wherein the annular space (4) is traversed in its upper part by the inner tube (5) which passes through the outer tube (6), which leads to use two systems of deflectors (7) identical and operating in parallel, equivalent to the case of an annular space divided into two sectors. 30 4) Filling device according to claim 1, wherein each baffle (7) has the shape of a wing inclined downwards by an angle alpha with respect to the vertical between 300 and 50 °, each deflector occupying a portion of the horizontal surface of the sector comprised between 50% and 90% of the said area of the sector. 5) Filling device according to claim 4, wherein when the diameter of the wall of the annular space (4) varies, due to outer tube portions (6) of decreasing diameter from top to bottom, the system of deflectors (7) adapts to this variation of section while always respecting the occupation condition of said horizontal section in the range of 50% to 90% by an adjustment of the angle alpha, the smallest value being adapted to the portion of smaller diameter, and the largest value at the portion of larger diameter, the articulation of the blade of the deflector on its vertical axis being free, and a second set of chain to raise more or less the end of the blade of the deflector so as to vary the angle alpha. 6) filling device according to claim 1, wherein when the diameter of the wall of the annular space (4) varies, due to outer tube portions (6) of decreasing diameter from top to bottom, the system of deflectors (7) is provided at its ends closest to the wall of the annular space (4) rubber lips that adjust the length of the blades so as to maintain the occupancy factor of the section of the annular space in case of variation of the internal diameter of the outer tube of the bayonet. 7) Method of loading the catalyst using the device according to claim 1 characterized by the following steps: the loading system is initially wound in the outer reel (10), the hopper (1) being filled with solid, the loading system is then gradually introduced into the annular zone (4) at its upper part until the first deflector (7) reaches a distance from the bottom of the tube of between 50 cm and 100 cm. the conveyor belt (2) is started so as to provide a solid flow rate of between 250 and 500 kg / h, which solid is introduced into the annular zone (4) or a sector of said annular zone (4) by through the funnel (3), as the tube is filled, the loading system is raised from the annular zone (4) with the aid of the external winder (10), so that to respect one. Constant distance between the first deflector and the surface of the bed which is constituted progressively, said distance being between 50 cm and 100 cm. the system is wound with a speed equivalent to the tube loading speed of between 0.2 meters / min and 0.4 meters / min. once the tube is loaded and the loading system is wound up, the system is moved for loading the next tube.